1. Field of the Invention
The present invention relates to an image display apparatus that is a so-called head mounted display or the like.
2. Related Background Art
For image display apparatuses such as head mounted displays, various types of optical systems have been proposed for miniaturizing each whole apparatus. For example, Japanese Patent Application Laid-Open No. 7-333551 (corresponding to EP 687932A3) discloses an apparatus in which a prism-like optical element consisting of rotationally asymmetrical first, second, and third surfaces is used to display an image on a display surface of an image display element as an enlarged image via the first, second, and third surfaces of the optical element.
Such a prism-like optical element makes it possible to correct image distortion, curvature of field, and astigmatism with a very compact, simple arrangement, and satisfy the telecentric condition with respect to the display surface.
Although transmissive liquid crystal displays were common as image display apparatuses at the time of the proposal in this reference the transmissive liquid crystal display has drawbacks that it is difficult to make the increase of pixels be compatible with miniaturization since the pixel apertures in the transmissive liquid crystal display are small. Recently, since high-resolution image output apparatuses such as personal computers, and DVDs besides moving image apparatuses such as VTRs, and TV sets have increased, high-resolution image display is desired.
Corresponding to such a current status, it is possible to obtain a high-resolution image by using a reflective liquid crystal display whose pixel apertures can be made to be large while attaining the increase of their pixels and miniaturization. An apparatus using a reflective liquid crystal display is disclosed, for example, in Japanese Patent Application Laid-Open No. 11-125791. This reference, as shown in FIG. 15, discloses a display apparatus in which a reflective liquid crystal display 103 is directly illuminated with illumination light 102 from a light source 101 without mediacy of an optical element and an image on the liquid crystal display is guided to an observer""s eye 105 to be displayed as an enlarged virtual image by a prism-like display optical element 104.
However, in this display apparatus, since the liquid crystal display 103 is directly illuminated with the illumination light 102 from the light source 101, an angle xcex8 of the illumination light 102 and a normal of the liquid crystal display 103 becomes large.
For this reason, since the whole display apparatus becomes large and the liquid crystal display 103 is greatly inclined relative to the display optical element 104, a distance between the liquid crystal display 103 and the display optical element 104 changes depending on places, and there is a problem that optical characteristics degrade.
Moreover, another display apparatus disclosed by Japanese Patent Application Laid-Open No. 11-125791 has a configuration that, as shown in FIG. 16, a light source 101 is provided on the opposite side of the reflective liquid crystal display 103 with respect to the prism-like display optical element 104, the liquid crystal display 103 is illuminated with the illumination light 102 from the light source 104 and reflected by the liquid crystal display 103, and the reflected light from the display is adapted to enter an observer""s eye 105 through the inside of the display optical element 104 again.
However, since the utilization efficiency of the illumination light is not taken into account in such a conventional illumination system and some amount of light emitted from the light source is not used as illumination light, the illumination systems shown by these conventional examples are very inefficient.
An object of the present invention is to provide an image display apparatus using a reflection type display device corresponding to high-resolution images such as a personal computer output, and having high utilization efficiency of illumination light though it has very simple and compact configuration.
In order to attain the above-described object, an image display apparatus according to one embodiment of the present invention comprises a light source which supplies illumination light, a reflection type display device which reflects the illumination light and modulates the illumination light into image light, an illumination optical system which guides the illumination light to the reflection type display device, and a projection optical system which guides the image light to an observer. The image display apparatus is characterized in that the illumination optical system comprises a first optical member that directs the illumination light toward the reflection type display device, and a second optical member that directs the illumination light toward the first optical member.
Moreover, an optical system according to another embodiment of the present invention has an illumination optical system that guides illumination light toward a reflection type display device, and a projection optical system that guides the image light, reflected by the reflection type display device, to an observer. The optical system is characterized in that the illumination optical system comprises a first optical member that directs illumination light toward a reflection type display device, and a second optical member that directs the illumination light toward the first optical member.
Moreover, an image display apparatus and an optical system according to an embodiment of the present invention are characterized in that, in particular, a second optical member satisfies at least one of: (a) a condition that the second optical member comprises a secondary light source generating part which generates a secondary light source with illumination light emitted from a light source, and a reflecting surface which guides illumination light other than the illumination light directly incident on the secondary light source generating part among the illumination light from the light source, to the secondary light source generating part, and emits the illumination light from the secondary light source to the first optical member; and (b) a condition that the second optical member comprises a reflecting surface which deflects a principal optical path of the illumination light from the light source, and emits the illumination light, reflected by the reflecting surface, to the first optical member.